New Advent refoaming - how to reach cone's underside?

[Sensible]

A couple years ago I ordered replacement foam surrounds from SimplySpeakers.com, for my 1978 New Advents. I took them out of service, but am just now getting around to the job.

The original foam was glued to the underside of the cone, and I suppose that's the right way to attach these replacements. But is there a way to access the underside lip without removing the cone (which I do NOT want to do)? Will alcohol simply dissolve the old foam and give me a clean surface? Getting a clean surface and pressing the new foam uniformly to the underside seems my biggest challenge.

But I have a few other mysteries, too...

• The replacement surrounds are a dimensional match, except that the outside ring (1/2") is twice as wide as the original. I'd think I can just glue the excess up the surface of the basket?
  
• I'm planning to cut the dust cap except for a small hinge, and shim the coil before gluing to the basket. But I ordered replacement caps as a precaution. Any preference as to whether I should use the old ones or the new (the new ones are not an exact dimensional match.)
  
• One other concern is that maybe the speaker's having sat facing up for two years might have weakened the spider? When facing up, the cone's edge is slightly below the level of the basket's edge, when facing down, the cone's edge hangs slightly below (or rather, I mean above, except they're both upside down). Also, it seems to be very slightly tilted (one side's edge is more misaligned than the other's). Will the new surround correct this geometry?
  
• When gluing to the basket, I assume I should use some tissue or something to prop the cone up so the cone and basket edges are at exactly the same level? I've watched and read every video and instruction I can find, but have seen this measure taken only once.

Thanks for any insight you have. I'm looking forward to actually hearing my records again.

[Doug G.]

Welcome to the Advent Forum.

Simply Speakers sent you the wrong surrounds. You have ones meant for the original masonite woofers. They have the larger flange around the outside to glue to the masonite ring.

However, they will sort of work for all-metal Advent woofers but, because the flange will not fit onto the ~1/8" ridge, they have a tendency to want to wrinkle as the flange lays on the angled part of the frame.

You should trim the outside flange to fit the ridge if at all possible. It will make the install much easier. That or get the correct surrounds.

I use lacquer thinner rather than alcohol to clean the cone edge. It cuts the previous foam and glue better. The main thing is to get a smooth surface even if you can't completely remove all of the residue.

I have used two methids to glue the surround to the underside of the cone edge. You can have the edge of the surround laying on the top edge of the cone and apply the glue to the top of the surround flange and then push the surround lip down under the cone edge. Usually, it will slip under there without too much of a mess.

The other way is to put the surround in position under the cone edge and press it down as you apply glue to the top of the surround flange, letting it back up against the underside of the cone edge.

I have never shimmed the VC when I refoam Advents but if you want to, it doesn't make any difference which dust cap you put back on there as long as the new one is gauze like the original.

I wouldn't worry too much about the spider sag unless it's really bad. It's natural for them to have loosened up over the years from flexing. Just refoam and they will probably be fine.

Don't use tissue to prop the cone. It may put uneven stresses on it and cause it to not really be centered. Just use the glue and keep working the edges as the glues sets enough to hold everything in place.

Doug

[DON]

Welcome to the Advent Forum.

I have replaced the surrounds on a few Advents and Doug has given you good advice. I tried the surrounds from Simply Speakers and they sent me the same ones you describe with the wide outer edge. I couldn't get the cone to center correctly and finally gave up and removed the foam. I ordered another set from Rick Cobb "LooneyTunes" on e-bay and he sent the proper surrounds. They have a larger roll and the flanges are narrower than the ones from SS and to me they seem more flexible. Rick also sends a cd with a 30hz tone if you want to use that method for centering the cone.

I came to the conclusion that removing all the glue from the underside of the flange is near impossible. I just remove all the old surround to get a reasonably smooth surface to attach the new foam edge to. I lay the new foam on a flat surface and apply the glue to the inside edge with my finger or a small brush (acid brush). It doesn't take much as long as all surfaces of the flange are covered. The foam can be slipped under the cone without making a big mess. I try to center the foam on the cone and begin pressing the cone into the foam and supporting the foam from the bottom with my finger. After the glue is dried I add a small amour of glue in an even ring around the cone and work in under the cone filling any voids.

Welcome and good luck! There's plenty of help here.........I'm a newbie and these guys have been very gracious in helping me.

[Sensible]

Thanks to both of you.

Your techniques for applying the glue both seem good to me, but getting the old crud off still seems problematic (or after alcohol or lacquer thinner, does the old foam just wipe away?)

I spoke with a tech rep at Simply Speakers. (I'll omit his name in case I misunderstood something.)

He advises to attach the surround to the top of the cone, that it won't make any difference sonically. In fact, now that I read their generic instructions with new eyes, I see it's Step 6:

"Work new edge to cone for several minutes and allow to dry for one hour. It is easier to install new edge to the TOP of cone regardless of original location. Performance is not affected either way."

That seems sensible, but I'm concerned that I haven't seen anyone else advise this for New Advents anywhere. And why didn't Advent attach it to the top?

Does everyone agree that attaching to the cone's top is okay?

He also says that they use the same surround for both the New Advent and the original Advents, and they don't trim it, but I can trim it if I want. (I find it hard to believe that customers don't notice the visual difference, so maybe I misheard.) I think I'll conservatively trim it. I agree that, if only theoretically, an angled surface and a flat, round part don't to go together geometrically, and it's only because rubber stretches that untrimmed could work.

He concurs that I don't need to bother with shims, if I test the freeplay as I go, by pressing on one side of the cone listening for scrape, then on the other, and so on, N, S, E and W. (Their glue gives about 5 minutes of work time.) Not sure I fully understand how to adjust for a scrape if I hear it, but let's see if I can figure it out in that time.

He also says they run a tone sweep when they're doing this in-house, and advises also to use various frequencies -- it could be okay at 30 Hz but show a problem with 120. I suppose I can make myself a CD using my computer DAW software. Considering that cutting the dust cap probably invites its own set of novice errors, I'll skip shimming.

The only question left is how to work with my fingers crossed. ;-)

[JKent]

Hi Sensible

You should not use generic foams on Advent speakers and you SHOULD shim them. This seller is the BEST (IMHO):

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330426747563

Read his Advent surround description and email him if you have questions. He will be a great resource. You can also look at his website for step-by-step refoam instructions.

Kent

[Doug G.]

Ah, some of these generic speaker techs...what can ya do?

It seems some of them take pride in advising people in the wrong ways of doing things on specific speakers.

It may be that the Advent woofers will work fine with the surround on top of the cone but the optimum way is with it underneath (for the all-metal woofers - the masonites are the opposite). Advent did it that way to put the cone in correct rest position for equal excursion.

Anyway, ignore that tech and do it the right way.

I also think it's cheap and misleading of Simply Speakers to supply the same surround for both woofers. It would be fine the other way around, supplying the New Advent woofer surround for both since the narrower outside flange works well for both. But NOT supplying the original (masonite) Advent surround for both.

I also hear you on the too small roll. I've heard that before about Simply Speakers surrounds. And again - too thick and stiff. They miss on all three important aspects.

I think somebody there bought a bunch of those incorrect surrounds and are sandbagging.

OK, enough Simply Speaker bashing \:^).

Don has a good idea with putting an extra little bead of glue around the surround/cone seam for strength. I do that too with both types and if you can get it nice and even, it will look professional.

If Kent's link goes to a Rick Bobb (looneytunes2001) auction, yes he has the correct ones. EDIT: Oops, I see it goes to one by MSound which, even though I haven't used theirs, I trust these other guys that say they are good too.

The thing with checking for scraping is this: the spider already has the one end of the VC centered and we just have to make sure the VC is parallel with the pole piece down in there. So, by moving the cone around, you change the parallelism. Pressing down on the cone in different places around the edge puts slightly different forces on it and, if the VC is close to the pole piece at any place. It will rub with pressure put on the cone in some places and maybe not others. By getting the cone positioned so there is never any rubbing regardless of where you press on it, it is assured that the VC is centered and parallel to the pole piece.

I have always found that the Advent cones pretty much find the correct place to rest on their own without having to move them around much or force them any particular direction. Just keep checking for rubbing until the glue is well on the way to setting.

Doug

[JKent]

Here are step-by-step instructions showing how to refoam most speakers

http://www.citlink.net/~msound/refoam/

M_Sound will sell the RIGHT surrounds, dust caps and adhesive for your speakers.

Kent

[Sensible]

Well, I suppose I'm not going to miss the bit of money spent two years ago, so I'll probably start over with MSound. Have already started reading through their stuff.

Doug, I think it's Don you heard regarding the roll's size. But, by golly, now that I've got out my calipers, the original rolls appears to be 11/16" across, while the new one is 9/16". Thanks. The old surround seems pretty stiff itself, but with 30 years passed, they're hard to compare.

For the record, the SS dust caps are also geometrically different, and although they appear to be porous material, they have a concentric fiber pattern, not the linen-weave pattern of the old ones.

That all pretty well clinches it, doesn't it. SS might be correct in that my ears and discernment might never notice, but as the saying goes (and Doug G says), "... might as well do it right."

[Doug G.]

Yes, an 11/16" roll is correct. When you hold the surround in your hand, it should be droopy and very flexible. One of the stiff ones will pretty much hold its shape. When the correct surround is installed into the driver, there should be very little resistance to moving the cone. The spider will offer some resistance but the cone will still be relatively easy to move.

And the old surrounds will be stiff from drying out after initially turning gooey.

Once the driver is installed into the cabinet, there should be considerable resistance to pushing in on the cone because you are compressing the air trapped in the cabinet. There is a small, controlled leakage around the voice coil and through the porous dust cap. If the cone pushes in easily, it indicates a larger air leak, usually around the woofer flange. Hence the need for the Mortite.

It may be that different people may or may not be able to tell the difference between an Advent speaker with a stiff surround woofer or one with a correct surround but the lowest frequencies can't help but be improved by having the correct components in there. That is how they were designed, after all.

Doug

[Sensible]

Not to flog this issue too much, but maybe others would want to know -- I can make a CD with computer-generated tones. What frequencies should I use? Am thinking 30, 75, 125 and 200 Hz, 15 seconds of each, for 5 minutes. (Don't want to be distracted by "rewinding.") Can't do a gradual sweep, but can do any increment and duration.

Intending to record all frequencies at 0 db, but play them back at low volume. Might have to adjust the volume while playing, though -- of course to the ear the higher frequencies sound louder. Does that matter to the speaker?

[JKent]

Not to flog this issue too much, but maybe others would want to know -- I can make a CD with computer-generated tones. What frequencies should I use? Am thinking 30, 75, 125 and 200 Hz, 15 seconds of each, for 5 minutes. (Don't want to be distracted by "rewinding.") Can't do a gradual sweep, but can do any increment and duration.

Intending to record all frequencies at 0 db, but play them back at low volume. Might have to adjust the volume while playing, though -- of course to the ear the higher frequencies sound louder. Does that matter to the speaker?

The M_Sound kit comes with shims and dust caps. No need for test tones

Kent

[Sensible]

Thanks again. I forgot that tones and shims don't mix.

Will report back when completed.

[Doug G.]

Hehe, I don't use either.

Doug

[Pete B]

18 Hz and don't use shims. Keep the original dustcaps, they are

critical for speakers that are used far beyond their piston range.

You want to drive them at their free air resonance where they

move very easily and do not require a lot of power.